This invention relates to spring suspensions for vehicle seats.
It is well known to provide a spring suspension for a vehicle seat, the suspension comprising a seat frame and a base frame interconnected by a scissor-action linkage arm system, the system including two pairs of scissor-action linkage arms spaced apart on a common pivot axis, said arms having pivotal interconnections at their opposite ends with said frames, to permit the frames to move towards and away from one another, each pivotal connection on one pair of arms being coaxial with a corresponding pivotal connection on the other pair of arms, and a biassing spring connected between parts of the suspension which pivot relatively to one another during relative movement of the frames towards or away from each other, to bias the two frames away from one another. A vehicle seat incorporating such a suspension is described in U.S. Pat. No. 3,109,621.
Such a vehicle seat spring suspension is very effective in isolating the seat occupant from vibrations transmitted in a vertical direction from the base frame to the seat frame, but has little if any effect on vibrations transmitted between the base frame and seat frame in a direction longitudinally of the suspension (i.e. in the fore-and-aft direction). The seat occupant can be isolated from such longitudinal vibrations by mounting the seat suspension on a mechanism designed to isolate longitudinal vibrations, but such a mechanism increases the space necessary to accommodate the seat and adds considerably to cost.
There is therefore a requirement, in a spring suspension of the type described, for simple and inexpensive means for damping vibrations transmitted between the base frame and seat frame in the longitudinal direction.